Fisch EEG Primer Chapter 6 Flashcards
EEG Artifacts
Physiologic Artifacts can be divided into two categories:
- Movements
- Bioelectrical Potentials
Non-physiological Artifacts arise primarily from two sources:
- External electrical interference
- internal electrical malfunctioning
A medium to high amplitude potential that only occurs at ONE ELECTRODE is…
artifact until proven otherwise
Rythmical/Simultaneous waveforms that appear in unrelated head regions are likely…
artifact since evolving electrographic seizures spread to adjacent leads and do not “jump”
Blinking artifact and other eye movements causes the most prominent changes in which leads…
vertical eye movments Fp1/Fp2 and horizontal movments in F7/F8 - downward deflections are typically noted as the positively charged cornea causes input 1 to be relatively positive compared with input 2
Describe a lateral rectus spike…
On occasion, prior to lateral eye movements, a preceeding single sharp muscle spike may be seen. - this may mimic abnormal epileptiform activity
Eye movement artifacts should be most/least prominent in which distributions
More promonent frontally and less prominent posteriorly - increased amplitude posteriorly should raise a “red flag” for alternative explanation
What are some causes of asymmetric eye movement? (4)
- decreased movement of one eye
- absence or destruction of an eye
- asymmetric electrode placement
- frontal skull defect ((lower in amplitude ipsilateral to defect)
Muscle artifact differ from cerebral spike discharges in that…
muscle artifacts tends to be of decreased duration
Reducing high frequency filter setting for high frequency muscle artifact my complicate the recording because…
changes the form of the waves so that a single potential may have the appearance of a a spike
heart beat artifact can often beating eliminated by…
combining ear leads or a balanced neck/chest reference montage
Pulse wave artifact is caused by…
temporary changes in electrical contact as pulse wave travels past electrode. Typically frontal/temporal distribution millisec following ECG tracing.
Perspiration artifact consists of…
slow waveforms (usually greater than 2 sec in duration) - perspiration changes impedence contact between skin and recording electrode AND slowly changing potentials generated at the sweat glands.
How can perspiration artifact be reduced..
cooling the patient and drying the scalp with fan or alcohol
Sympathetic skin response (SSR) also known as the galvanic skin response consists of…
slow waves 0.5-1 sec that last 1.5-2 sec with 1-3 prominent phases. Represents an autonomic response medicated by cholinergic neurons in response to sensory or psychic stimulus.
What distribution is the sympathetic skin response typically found?
frontocentral channels in longitudinal bipolar montages and a characteristic triple phase reversal in transverse bipolar montages - best monitored by un-abraded palmar and dorsum of hand recording.
Movement of the tongue (glossokinetic) and other oropharyngeal structures may result in…
wide spread slow waves of maximal distribution in longitudinal bipolar montages in middle of head
Palatal myoclonus generally causes…
rythmical muscle artifacts at about 60-120/min seen only in referential montages and persist in sleep - appears as fast paired deflections.
Tongue movement artfacts can be identified on routine EEG by asking the patient to repeat..>
“Lilt”, “TomThumb”
Dental restorations WITH dissimilar metals may cause what types of artifact
may cause artifacts when metal touches commonly caused by speaking or chewing.
Two common types of interference are from…
electrostatic (e.g. unshielded power cables) and electromagnetic (e.g. large flow going through cables or transformers)
